Electric heating unit and method of manufacturing same



April 1933- A. w. WALKER ET AL ,905,770

ELECTRIC HEATING UNIT AND METHOD OF MANUFACTURING SAME Filed July 3,1929 2 Sheets-Sheet l t o 14 H y 4 i /Z 12 1/ 3 a f I 3 INE 0R8 M, Z. gy W 'ATTOR z' April 25, 1933. A. w. WALKER ET AL ELECTRIC HEATING UNITAND METHOD OF MANUFACTURING SAME Filed July 3, 1929 2 Sheets-Sheet 2 INVENT ORS LT M ATTO Ex Patented Apr. 25, 1933 UNITED STATES PATENT OFFICEARTHUR W. WALKER, MALDEN, AND ALBERT L. SMITH, OF WEST MEDWAY, MASSA-CHUSETTS, ASSIGNORS TO WALKER & PRATT IVIFG. 00., OF BOSTON, MASSACHU-SETTS, A CORPORATION OF MASSACHUSETTS.

ELECTRIC HEATING UNIT AND METHOD OF MAIVUFACTURING SAME Applicationfiled July 3, 1929.

This invention relates to electric heating units and to the manufactureof apparatus of this character. The invention will be herein disclosedas embodied in a heating unit designed especially for use in electricranges, although it is contemplated that the invention may also be usedin other forms of apparatus.

It is the chief object of the invention to devise an exceptionallysturdy and reliable device of this character, to provide for theconvenient replacement of the heating conductor, and to simplify themethods of manufacture of apparatus of this type. The invention aimsespecially to improve the mounting in their supporting structure of theinsulating bushings which carry the elec tric heating conductor.

The nature of the invention will be readily understood from thefollowing description when read in connection with the accompanyingdrawings, and the novel features will be particularly pointed out inthe-appended claims.

In the drawings,

Figure 1 is a perspective view of a heating unit constructed inaccordance with this invention, the unit being shown upside down;

Fig. 2 is a vertical central sectional view of the unit shown in Fig. 1;

Fig. 3 is a perspective view illustrating a step in the method ofmanufacture of the unit; and

Fig. 4: is a perspectiveview of one form of insulating bushing which maybe used in the unit.

The particular unit shown is designed for use in electric ranges andincludes a top plate 2 having a series of webs or flanges 3 integraltherewith and extending from the lower side thereof. This top plate isof circular form and it includes an integral marginal flange or rim 4:projecting from its edge and surrounding the other parts of the unit. Abottom plate5 fits into the lower end of the rim 4 and normally issecured to the plate 5 by a screw threaded stud 6 and nut 7. The flanges3 carry a series of insulating bush ings made of somerefractoryinsulating material such as lava, soapstone, steatite, ortheSerial No. 375,750.

like, and the electric heating conductor 9 is threaded through thesebushings and is supported in its operative position by them. Theseflanges thus form, in effect, a supporting grid for holding the heatingconductor wire being coiled so that a relatively long length is disposedin the comparatively small space provided in the top plate. The twoleads a and 1) near the perimeter of the unit are led through insulatingbushings 10 and 12, respectively, in the bottom plate ,5, and aremechanically secured to, but insulated from, lugs 18 and 14,respectively, which are cast integral with the plate, these lugs beingprovided with'clamping bolts 15 and 16, re-

spectively, for this purpose. The two leads a and b which are locatedadjacent tothe central part of the unit are both led through aninsulating bushing 17 secured in the bottom plate 5 and are fastened toa bolt 18 which is secured in, but insulated from, a 7

lug 19 integral with the plate, in the same manner that the other leadsare, fastened to the bolts 15 and 16, respectively. The current supplywires also are secured to'these same bolts, the arrangement usuallybeing such that the two sections of the heating conductor or coil may beconnected in parallel or series, as desired. In assembling the bottomplate to the top plate the position of the former plate is determined bya lug 24:, Fig. 1, which enters a notch (not shown) in the edge of thebottom plate 5. Ears 25 project from the edge of the bottom plate andare located in notches 26 formed to receive them in the edge of the rim4, each of these ears being drilled and tapped to receive screws bymeans of which the unit may be secured to additional parts of a range. 1

The mounting of the insulating bushings 8 constitutes an importantfeature of this invention. Preferably this is accomplished by making thetop plate 2 and the ribs or flanges 3 integral with each other by ametal casting process and supporting the bushings in the mold in such amanner that they will be cast into the flanges 3 and subsequently heldsecurely in this position by the shrinking of the metal around them.This may be done in several ways, but a convenient method consists insupporting the bushings inasandcore, such as that shown at 20, Fig. 3.This core may be made in the same way as those commonly used in casting,suitable slots or spaces, such as those shown at 21, being left for theflow of the metal. The ends of the bushings are protected by the core sothat metal cannot flow into them or cover them, and the threaded stud 6may or may not be supported in the core, as desired. The method ofmaking a core of this construction will be obvious to those skilled inthe art of metal casting. This core after being baked with the bushingsin it is placed in the sand in a casting flask, a suitable cavity beingmade in the sand by means of a pattern to provide for the casting of thetop plate 2 with its ribs 3 and peripheral flange et. The melted metalflows around the bushings, completely encir cling them, and as it coolsit shrinks and anchors the bushings securely in the flanges. The coredisintegrates in the casting operation, or the binder holding the sandparticles together is destroyed, so that any remnants of the core areeasily disposed of.

The bushings 10, 12 and 1'? in the bottom plate 5 preferably are castinto this plate in the same general way. The mounting of these bushingsfor the casting operation will be obvious to those skilled in the art ofcast- This method provides an economical way of handling the relativelylarge number of bushings required in a unit of this kind, and produces afinal structure which is very sturdy and reliable and which requiresrelatively little labor in assembling. A slow depreciation of the coilor heating conductor occurs in use so that it becomes necessary after atime to renew it. This can readily be done by taking the unit out of therange, removing the bottom plate, taking out the worn out coil andthreading in a new one. The construction is of further advantage inaffording ve complete protection for the coil, while at the same timeproviding a smooth top surface on the unit for the support of cookingutensils.

In some cases it may be desirable to roughen, groove, or recess thecentral port-ions of the bushings, as shown for example at 22, Fig. 4,so as to give the casting metal additional anchorage in the bushings andto prevent any possibility of endwise movement of the bushingsrelatively to their support without destroying them. This, however, isnot usually necessary.

While we have herein shown and described a preferred embodiment of ourinvention and a typical method of making it, it will be understood thatthe invention may be embodied in other forms without departin from thespirit or scope thereof.

TIaving thus described our invention, what we desire to claim as new is:

1. In an electric heating unit, the combi nation of an electric heatingconductor, a plurality of insulating bushings arranged in spacedrelation through which said conductor extends and in which it issupported, and a metal support carrying said bushings and shrunk onthem, thereby to hold the bushings in place.

2. An electric heating unit comprising a cast metal plate havingintegral flanges projecting from one side thereof, insulating bushingscast in said flanges and held in position by the shrinking of the metalon them, and an electric heating conductor extending through saidbushings and supported by them in its operative position.

3. An electric heating unit comprising two metal plates secured togetherin substantially parallel spaced relationship, a cast metal grid betweensaid plates, refractory insulating bushings mounted in said grid andheld therein by the shrinking of the metal of the grids on them, and anelectric heating conductor threaded through said bushings and supportedby them.

a. That improvement in methods of making electric heating units whichconsists in supporting a plurality of refractory insulating bushings inposition for casting, and casting a met-a1 part for one of said unitsaround said bushings but leaving the ends of the bushings exposed,whereby the shrinking of the metal upon cooling will lock said bushingssecurely in said part, and thereafter placing an electric heatingconductor through said bushings.

5. That improvement in methods of mak ing electric heating units whichconsists in making a casting core with a plurality of insulatingrefractory bushings supported in it, and casting a metal part for one ofsaid units on said core and around said bushings, whereby the shrinkingof the metal around the bushings when it cools will hold the bushingssecurely in said part, and thereafter placing an electric heatingconductor through said bushings.

6. That improvement in methods of making electric heating units whichconsists in making a casting core with a plurality of refractoryinsulating bushings supported in it in such positions that the ends ofthe bushings are protected by the core, casting on said core a metalpart for one of said units, and during said casting operation causingthe metal to flow completely around said bushings except at their ends,whereby the subsequent shrinking of the metal upon cool ing will locksaid bushings securely in said part, and thereafter placing an electricheating conductor through said bushings.

7. In an electric heating unit, the combination of an insulating bushingand a flanged metal support cast therearound, said bushing extendingthrough a flange of said support and held rigidly therein by theshrinking of the cast metal around the bushmg.

8. In an electric heating unit'the combination of an electric conductor,a series of insulating bushings arranged in spaced relation andsupporting said conductor, and a metal support cast around saidbushings, said bushings extending through and being held rigidly in saidsupport by the shrinking of the cast metal around them.

9. In an electric heating unit the combi nation of an insulating bushingfor supporting an electric heating conductor, and a metal support inwhich said bushing is mounted, the metal of said support being castaround said bushing and holding it securely in place, said bushinghaving a recessed outer surface in contact with the cast metal, wherebythe cast metal entering said recessed surface serves to resist endwisemovement of the bushing relatively to said support.

10. An electric heating unit comprising a cast metal plate havingintegral flanges projecting from one side thereof, insulating bushingscast in said flanges and held in position by the cooling and shrinkingof the cast metal on them, said bushings extending through the flanges,and an electric heating conductor extending through the bushings andsupported thereby in operative position.

11. An electric heating unit comprising a top metal plate, a series ofmetal flanges at the lower side of said plate, bushings of refractoryinsulating material extending through said flanges, the metal of saidflanges being shrunk on the bushings and serving to hold them securelytherein, and an electric heating conductor threaded through saidbushings and supported thereby in operative position.

12. An electric heating unit comprising two metal plates securedtogether in substantially parallel spaced relationship, a cast metalgrid between said plates, refractory insulating bushings mounted in saidgrid and held therein by the casting of the metal of the grid aboutthem, and an electric heating conductor threaded through said bushingand supported thereby.

13. An electric heating unit comprising top and bottom metal plates, aplurality of metal flanges integral with one of said plates andprojecting into the space between them, bushings of refractoryinsulating material mounted in said flanges, the metal of said flangesbeing cast about the bushings and serving to hold them securely inplace, an electric heating conductor threaded through said bushings andsupported thereby in operative position, means for removably securingsaid plates together, and a rim carried by one of said plates andencircling said conductor, said rim and platesserving to substantiallyenclose said conductor.

14. That improvement in methods of making electric heating units whichconsists in supporting a plurality of refractory insulating bushings inposition for casting, and casting a metal grid for one of said unitsaround said bushings, while leaving the ends of the bushings exposed,whereby the shrinking of the metal upon cooling will lock the bushingssecurely in said grid; and thereafter mounting an electric conductor insaid grid supported bushings.

15. That improvement in methods of making electric heating units whichconsists in making a casting core with a plurality of insulatingrefractory bushings supported in it, and casting a metal grid for one ofsaid units on said core and around said bushings whereby the shrinkingof the metal around the bushings when it cools will hold the bushingssecurely in said grid; and thereafter mounting an electric conductor insaid grid supported bushings.

16. That improvement in methods of making electric heating units whichconsists in making a casting core with a plurality of refractoryinsulating bushings supported in it in such positions that the ends ofthe bushings are protected by the core, casting on said core a metalgrid for one of said units, and during said casting operation causingthe metal to flow completely around said bushings except at their ends,whereby the metal upon cooling will lock the bushings securely in saidcast grid, and thereafter mounting an electric conductor in said gridsupported bushings. I

In testimony whereof we have hereunto signed our names to thisspecification.

ARTHUR W. IVALKER. ALBERT L. SMITH.

